The Earth in Space
Our solar system is located in a benign region of the Milky Way galaxy, such that Earth is not bombarded with excessive high energy radiation from stellar neighbors. Within our solar system, Earth is positioned at just the right location with respect to Sol (our sun) to enable water to exist in all three phases. Sol itself is a stable, middle-aged star with no recent history or inclination to surprise it's planets with radical changes in energy output. These external factors are critical for creating a haven for life in the harsh environment of space. Our celestial neighborhood is a good one, but what about our home planet itself?
Solar System Calculators (more info)
The Animated Virtual Planetarium ( This site may be offline. )
Build Your Own Solar System (more info)
Learning about tides (link to external site) (more info)
Sun-Earth-Moon Geometry (link to external site) (more info)
The Seasons and Earth's Orbit (link to external site) (more info)
Sun Path Activity (more info)
- Solar System Calculators (more info)
Comparing the Inner Planets
Mars offers the most intriguing comparison with Earth. Though only half the diameter and twice the distance from the sun as Earth, Mars supports a thin atmosphere of mostly carbon dioxide, with temperatures that may occasionally be warm enough to melt water (which would instantly boil away to vapor in the extremely low atmospheric pressure). Martian seasons and the length of day are very near to Earth's, producing polar caps that shrink and grow, dust storms, frost patches and seasonal clouds that mimic Earth. There is every indication that the surface of Mars supported vast oceans of liquid water at some point in its distant past, when it still had an atmosphere dense enought to trap solar energy. Stream channels (link to external image) (more info) , flood plains and indications of ancient shorelines sprawl in desiccated testimony to the past, and fuel the hopethat life may once have existed there during warmer times. Huge amounts of water may yet remain on Mars, frozen as permafrost beneath the surface. Mars beckons, and the 21st century opens with a fleet of spacecraft missions (link to external site) (more info) poised to unlock the mysteries of the planet's history.
Returning to Earth, we are reminded once again of the cosmic confluence of factors that contribute to our currently comfortable planetary situation. But indeed, if it were not so, we would not be here to reflect upon or examine the details of the Earth system ...